1. Field of the Invention
The present invention relates to a membrane electrode assembly for a fuel cell, a fuel cell, and a fuel cell system, which have an anode catalyst layer.
2. Description of the Related Art
A membrane electrode assembly for a fuel cell generally includes an ion conducting membrane that has two sides in the thickness direction, an anode catalyst layer laminated on one side of the ion conducting membrane, a cathode catalyst layer laminated on the other side of the ion conducting membrane, an anode diffusion layer laminated on the outer side of the anode catalyst layer, and a cathode diffusion layer laminated on the outer side of the cathode catalyst layer.
An anode fluid supplied to an anode may contain carbon monoxide that interferes with catalytic activity in the catalyst layer. In this case, as the duration of power generation increases, catalytic activity gradually reduces. This may cause a decrease in power generated by the fuel cell.
In light of the above situation, Japanese Patent Application Publication No. 8-203537 (JP-A-8-203537) describes a fuel cell that includes a membrane electrode assembly in which a layer that oxidizes carbon monoxide is provided at portion of the catalyst layer, adjacent to the diffusion layer.
In addition, Japanese Patent Application Publication No. 2004-186049 (JP-2004-186049) describes a membrane electrode assembly in which, focusing on porosity, both an anode catalyst layer and a cathode catalyst layer each have an increased porosity at a portion adjacent to a diffusion layer. Furthermore, Japanese Patent Application Publication No. 7-85874 (JP-A-7-85874) describes a membrane electrode assembly in which the amount of ruthenium supported is greater at the downstream side than at the upstream side to thereby suppress carbon monoxide (CO) poisoning at the downstream side.
According to the above described technologies, when the duration of power generation extends over a long period of time, a decrease in power generated by the fuel cell can be somewhat suppressed but it is not sufficient.